40 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



ever, in their adaptation to environment. Many of them are not only 

 parasitic but so closely adapted to parasitizing particular host-species 

 as not to be found elsewhere. Others attack several or many species, 

 usually related. Even among saprophytes many species are found only 

 upon particular forms of deca3dng animal or vegetable matter. The 

 great economic importance of these parasitic and closely adapted sapro- 

 phytic species has been recognized by the de\^elopment in recent years 

 of the literature of plant pathology (phytopathology). These cannot 

 be considered in this work. 



Cytology op Molds* i 



General Structure of Molds. — Three kinds of cell-structure 

 formation are found in molds: 



1. Some, belonging to the Phy corny cetes, show no cross-walls; they 

 have a much branched, felted mycelium, but in the early stages there 

 are no true transverse septa. Septa appear in many forms only when 

 fruiting begins, but in the opinion of some they merely separate the 

 living portions of the mycelium from those in which the cytoplasm is 

 dead or degenerating. The cytoplasm in the unseptate mycelium forms 

 one continuous mass; it contains a great many nuclei (Fig. 23, i and 

 2). Each nucleus with the cytoplasm surrounding it, according to 

 Sachs, may be considered a physiological unit acting in a somewhat 

 similar capacity as a cell, or may be designated as an energid. This 

 view is not held by all observers, however. Considered thus, the 

 mycelium represents the collection of a great many indistincts cell 

 which are not separated by walls. The Mucorinea, for example, belong 

 to this structural type. 



2. Other fungi, especially among the Ascomycetes, have a septate 

 mycelium, but one in which the transverse septa do not restrict cellular 

 functions as true cells. It consists of compartments containing a 

 variable number of nuclei called coenocytes {Fig. 24, i). Each compart- 

 ment may be considered, not as a true cell, but as a colony of rudi- 

 mentary cells, energids. 



3. Still other molds have a mycelium consisting of true cells with 

 a single nucleus, as for example Endomyces fihuliger (Fig. 24, 3 and 4) 

 and Endomyces decipiens. 



* Prepared by A. GtiillierMond. 



